1. Field of the Invention
The present invention relates to a sheet feeding device including a sheet cassette in which recording media such as sheets are stacked and an image forming apparatus.
2. Discussion of the Background
In an image forming apparatus, such as a copier, a printer, a facsimile apparatus and a printing apparatus, an image formed by an image formation part thereof is transferred onto a recording medium such as a recording sheet conveyed from a sheet feeding device, and thereby a record output is obtained.
A cassette in which recording media are stacked is installed in the sheet feeding device, and the sheet feeding device is configured to feed out the recording media in the cassette.
Some cassettes are configured to accommodate recording media of a specific size. In this case, one cassette is necessary for each desired size of recording media, so that the procurement and operating cost of the apparatus is increased. Further, when the image forming apparatus is configured such that one cassette can be installed in the sheet feeding device, when use of a different size of recording media is desired a different cassette must be installed, which is troublesome. Even when the image forming apparatus is configured such that a plurality of cassettes can be installed in the sheet feeding device, often cassettes must be exchanged. Furthermore, because a cassette for recording media of a size that is used infrequently must be also procured, the procurement and operating cost of the apparatus is further increased.
Other cassettes are configured such that recording media of different sizes can be accommodated. In this case, recording media of a desired size is accommodated in the cassette.
Such a cassette capable of accommodating recording media of different sizes generally includes a size detect mechanism to detect the size of recording media stacked in the cassette. Japanese Patent publication No. 0292307 and Japanese Patent Laid-open publication No. 2002-096933 describe a size detect mechanism that determines the size of recording media stacked in a cassette by rotating a link member in conjunction with movement of an end fence regulating rear ends of the recording media and by measuring the rotation amount of the link member. The Japanese Utility Model Laid-open publication No. 06-001349 describes a structure in which the position of a side part of an end fence regulating rear ends of recording media stacked in a cassette is detected by a size detection device provided at one side end of the cassette in the widthwise direction of recording media and thereby the size of recording media stacked in the cassette is determined.
However, in the mechanism described in JP No. 0292307 and JP No. 2002-096933, the link member is relatively large in the widthwise direction of recording media and is rotated, so that the size of the cassette is inevitably increased. In the structure described in JP No. 06-001349 (U), because the size detection device is provided to one side end of the cassette, the size of the cassette in the widthwise direction of recording media is inevitably increased. Further, a size detection part is arranged at one side of the cassette in the widthwise direction of recording media and a contact pressure of the size detection device of the cassette relative to the size detection part is used in determining the position of the side part of the end fence. Therefore, if a contact condition of the size detection device relative to the size detection part is not appropriate, the position of the side part of the end fence cannot be correctly determined so that the size of recording media stacked in the cassette cannot be correctly determined. Further, in the mechanism in which the link member is rotated, a gap is generated between the link member and the cassette, so that the link member is easily deformed due to the contact pressure received from a size detection part, and there is a possibility that the link member is damaged at the end thereof. Further, because the link member is relatively large in the widthwise direction of recording media, the weight of the link member is increased, so that the operating force for the end fence is increased and the operability of the cassette may be deteriorated.